Adhesion refers to the state in which two surfaces are held together by attraction between molecules, atoms, and ions, and an adhesion phenomenon has been widely applied, from daily necessities such as tape, glue, and the like, to an automobiles and state-of-the-art semiconductor devices, in our lives. In recent years, along with remarkable development of industry, there have been various demands for adhesive from various fields.
Polymer adhesive can be classified into chemically reactive adhesive, solvent-based adhesive and hot melt adhesive depending on a solidification process. The hot melt adhesive of them is easy to use and is a representative example that can satisfy the recently emerging requirements for environment.
The hot melt adhesive is a material in a solid state at room temperature and is not dissolved or dispersed in a solvent, and it is used in a liquid state by melting only 100% solids with heat. The hot melt adhesive has illustrated a high growth rate as compared with the existing solvent-based adhesive due to its advantages of high productivity caused by process automation, eco-friendly characteristics, a wide range of applicability, a re-adhesion possibility, and the like, since DuPont first developed an ethylene-vinyl acetate (EVA) resin in 1960s. The hot melt adhesive is coated on an adherend surface while being in a molten state and is cooled and solidified by giving off heat to and around the adherend surface. The hot melt adhesive requires a small working space and has high-speed adhesion without a drying process as compared with other solvent-based adhesive or water dispersed adhesive. High-speed adhesion of the hot melt adhesive enables automation of a production line and an increase in productivity, and, thus, the hot melt adhesive has considerable economic advantages such as improvement in productivity, reduction of labor costs, reduction of an amount of material caused by regulation of spread, and the like. The hot melt adhesive has been applied to various fields such as packaging, bookbinding, construction, woodworking, automobile, textile, and electrical/electronic fields.
The conventional commercial hot melt adhesive is generally classified into ethylene-vinyl acetate-based adhesive, polyolefin-based adhesive, styrene block copolymer-based adhesive, polyamide-based adhesive, polyester-based adhesive, and urethane-based (reactive hot melt) adhesive depending on a basic resin used therein. The basic resin highly affects adhesion strength and cohesion strength, which are the most important properties of the hot melt adhesive. The conventional commercial hot melt adhesive contains a mainly petroleum-based material as a basic resin and thus is not sufficient in eco-friendly characteristics, and has a problem that manufacturing costs can be increased due to external causes such as instability in petroleum-based material supply and demand, exhaustion of petroleum-based materials, and the like. Therefore, considering eco-friendly characteristics, a stable supply of materials, and a gradual increase in production cost, it is necessary to replace the whole or part of a basic resin, as a major constituent of the hot melt adhesive, with infinitely renewable biomass, particularly starch.
Meanwhile, generally, a furniture board mainly made of wood is banded with finishing materials made of PVC, polypropylene, or ABS in order to improve an aesthetic feeling of a surface of the furniture board. When the furniture board is banded with the finishing materials, a finishing material bander called “edge bander” is used. The edge bander refers to a device for bonding an edge to a corner portion of the furniture board for improvement in the beauty of the furniture board. When a board such as plywood is cut and hot melt adhesive melt with heat (170 to 200° C.) in an adequate amount is coated on its cut surface, the edge bander is used to bond an edge made of a synthetic resin to the cut surface. FIG. 1 illustrates one of general using forms of hot melt adhesive and illustrates a status where a wood board and an edge are bonded to each other with hot melt adhesive. Herein, the wood board as an adherend is mainly hydrophilic and the edge is mainly hydrophobic. Thus, even if a considerable amount of a basic resin as a major constituent of hot melt adhesive is replaced with starch, the hot melt adhesive needs to increase adhesion strength between adherends having different properties. Further, in order to secure workability of hot melt adhesive, an increase in viscosity of the hot melt adhesive according to an increase in starch content needs to be regulated to an optimal level.